The present invention relates to a wet type image forming apparatus, and particularly to a circulation system for developing solution for the wet type image forming apparatus.
Apparatuses that transfer toner to a recording sheet to thereby form an image include, for example, a dry type image forming apparatus, which applies powder toner to a surface of a developing roller to form an image, and a wet type image forming apparatus, which applies developing solution containing toner in carrier solution to a surface of a developing roller to form an image. The toner employed in the latter apparatus is finer than that employed in the former. Accordingly, the latter provides an image of a higher quality. Further, the wet type image forming apparatus requires less toner for printing an image with and equivalent color density compared to the dry type image forming apparatus. Furthermore, the wet type image forming apparatus generally uses a lower temperature of heat than the dry type image forming apparatus when the toner on a surface of a recording sheet is fixed. Therefore, the wet type image forming apparatus is considered to be advantageous in cost-effectiveness and in energy-efficiency.
FIG. 5 shows an illustrative configuration of such a conventional wet type image forming apparatus, which is disclosed in Japanese Patent Provisional Publication P2001-22185A. The wet type image forming apparatus includes a first applicator roller 210, a second applicator roller 212, a developing roller 214, a photoconductive drum 218, a developing solution container 250, a developing solution supplier pump 252, and a developing solution supplying pipe 228. The developing solution, which is nonvolatile and highly viscid, is carried from the developing solution container 250 to a pit portion formed between the first applicator roller 210 and the second applicator roller 212 via the developing solution supplying pipe 228 by the developing solution supplier pump 252, so that a certain amount of developing solution is sustained as pooled developing solution 242.
The pooled developing solution 242 in the pit portion is applied to surfaces of the first applicator roller 210 and the second applicator roller as an applicator. The second applicator roller 212 is in contact with the developing roller 214, which is also in contact with the photoconductive drum 218, and as the second applicator roller 212 rotates, the developing solution is evenly applied to a surface of the developing roller 214. As the developing roller 214 rotates, a surface of the photoconductive drum 218 becomes in contact with the toner on the developing roller 214, so that the toner contained in the developing solution is stuck to the surface of the photoconductive drum 218 due to an electric field generated between the developing roller 214 and the photoconductive drum 218.
As shown in FIG. 5, the first applicator roller 210 rotates in a clockwise direction, whilst the second applicator roller 212 rotates in a counterclockwise direction. As the first and the second applicator rollers 210, 212 rotate in the respective directions, a level of a central portion of the developing solution may occasionally be raised to be higher than topmost portions of the first and the second applicator rollers 210, 212 due to excessive supply of the developing solution, and so on. In this state, when the first and the second applicator rollers 210, 212 stop rotating, the excessive amount of the pooled developing solution 242 may overflow from the pit portion and run down from one of or both ends of the first and the second applicator rollers 210, 212 (i.e., a left-hand end of the first applicator roller 210 and a right-hand end of the second applicator roller 212).
When the excessive developing solution runs down from the right-hand side of the second applicator roller 212, the developing solution reaches to the surface of the developing roller 214, which has been evenly applied a proper amount of the developing solution as a layer. Thus the layer of the developing solution may be spoiled, and an image forming operation may be affected.